Polishes are intended to be sacrificial coatings which protect the underlying substrate by sacrificially accepting and resisting marks, soils, scuffs, abrasion, and scratches encountered in the normal use of the substrate, and, when the useful or aesthetic life of the protective film has expired, the polish can be easily removed from the substrate, to be replaced with a new coating. Historically, removability has been provided for floor polishes by incorporating high levels of acid-functionalized monomers in the polymeric polish vehicle, or by the use of high levels of relatively high acid functionalized Alkali Soluble Resins (ASR's) as formulation adjuncts. However, if sufficient acid functionality was added to the polish polymer or polish formulation so that adequate long-term removability was attained, the resistance of the polish film to scrubbing with alkaline detergent solutions was greatly compromised. If the acid functionality in the polish polymer or the amount of ASR in the formulation was restricted to allow for aggressive cleaning operations, then long-term removability was greatly compromised.
A solution to this detergent resistance/removability balance problem was provided by the technology taught by U.S. Pat. No. 3,900,438, granted Aug. 19, 1975 to R. E. Zdanowski which used polish polymers containing pendant amino functionality, rather than acid functionality, so that the polish film is inherently inert to attack by alkaline detergent solutions. Removability in that system was provided by using an acidic stripper solution which forms hydrophilic salts in the film when the acidic stripper neutralizes the polymeric amines. Hydration of this salt results in swelling of the polish film so that it loses its resistance to mechanical abrasion and its adhesion to the flooring substrate, so the film is readily removed. This solution to the detergent resistance/removability balance problem was not commercially successful because of the high levels of very expensive amino functional monomers that were required to obtain films which were adequately sensitive to the acidic stripper solutions. If lower levels of amino functional monomers were incorporated into the polish polymer backbone, then it was necessary that the stripper solution be based on stronger acids, or more concentrated acid solutions, in order to obtain adequate removability. These alternatives are not acceptable because of the hazards associated with handling these more aggressive solutions, and because of the tendency of the stronger acid solutions to corrode furniture, particularly metal furniture, in the areas to be stripped of polish.
The dilemma of balancing alkaline detergent scrub resistance with long term removability was materially addressed and largely resolved by the now well known technology of latent transition metal complex crosslinking of floor polish polymers and formulations. This technology is taught in U.S. Pat. No. 3,328,325, granted Jun. 27, 1967 to R. E. Zdanowski, U.S. Pat. No. 3,308,078, granted Mar. 7, 1967 to J. R. Rogers and L. M. Sesso, U.S. Pat. No. 3,467,610, granted Sep. 16, 1969 to I. S. Fiarman, et al., U.S. Pat. No. 3,554,790, granted Jan. 12, 1971 to D. R. Gehman, et al., U.S. Pat. No. 3,573,239, granted Mar. 31, 1971 to R. E. Zdanowski, and U.S. Pat. No. 3,711,473, granted Jan. 16, 1973 to C. J. Oliver.
This transition metal complex crosslinking technology is based on the addition of a transition metal (usually Zinc) complex with lablie, volatile amine ligands to a preformed emulsion polymer which contains acid-functionalized monomers. As the technology is taught, during the emulsion polymer film formation process the volatile ligands are released from the complex, freeing the metal to react with and crosslink the acid functionality of the polymer by forming ionic or Coordinate covalent crosslinking bonds. This crosslinked acid functionality is insensitive to alkali, imparting resistance to alkaline detergents to the polish film. The crosslinks are reversible if an amine (such as ammonia, or preferably a lower alkanol amine) is present in the detergent solution. These modified alkaline detergent solutions are called polish strippers, since they impart removability to the polish film by removing the crosslinking metals and leave the polymeric acid functionality to react with the alkalinity of the detergent solution.
In the commercial practice of this technology it is generally understood that care must be taken in the selection of the metal complex ligands. If the ligand is not sufficiently lablie, such as in the case of bi- or poly-dentate ligands (for example triethylene diamine, or ethylene diamine tetra acetic acid), then latent crosslinking of the polymeric acid functionality will not occur during the relatively short time available for polymer and polish film formation. A detergent resistance removability balance will not be attained. Similarly, if the ligands selected are not sufficiently volatile to be lost from the complex during the film formation process (for example, with diethanol amine or trimethanol amine), then the metal will not be released from the complex and latent crosslinking of the polymeric acid functionality will not take place. The resulting films will not have a detergent resistance/removability balance. Conversely, as discussed in U.S. Pat. No. 3,308,078, if the ligand is too labile, such as in the case of stericly hindered amines (for example triethyl amine, or N,N-diethyl propyl amine), or if insufficient labile metal complexing ligand is present, then precrosslinking of the polymeric acid functionality with metal will occur before film formation. This was found to be undesirable, resulting in an emulsion polymer and polish formulation having an elevated minimum filming temperature (MFT), an increased requirement for organic solvents to act as plasticizing and coalescing agents, polymer emulsion instability, and a polish that did not readily form a tough, coherent, traffic-resistant coating. The lack of a coherent film reduced resistance to marking, soiling, scuffing, and abrasion, and poorer water resistance and detergent scrub resistance.
Although transition metal crosslinking of acid functionalized polish polymers provides a balance of detergent resistance and removability to the polish film, this advantage is offset by the deleterious effects of the metal crosslinking agent or the metal complex on the polish and polymer stability, polymer manufacturing ease and cost, and polish gloss. Furthermore, the high levels of volatile amine ligands charged to the polymer (in excess of the complex stochiometry to shift the complex formation equilibria toward the fully chelated metal so that precrosslinking of the polymer emulsion can be avoided) presents problems in polish formulating, handling, and application in the form of odor, toxicity, and poor polish recoatability. Also, the heavy metals used as the basis for the transition metal complex present environmental hazards in the disposal of unused or contaminated polish, emulsion polymer, and spent stripper solutions which contain removed polish film. Recently, heightened concerns regarding environmental safety and workplace safety have made latent metal crosslinkling less acceptable.